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CMOS active crystal oscillator supply voltage and output voltage:
The output voltage of the square wave (CMOS) active crystal oscillator is an AC signal, which includes a high level (Voh) and a low level (Vol), where the high level is approximately equal to its supply voltage (approximately equal to 90% Vcc).
Voh: Voltage output high
Vol: Voltage output low
Problems with using a multimeter to measure the output voltage of a CMOS active crystal oscillator
Generally speaking, the active crystal oscillator outputs a high-frequency square wave signal, and the AC range of the multimeter is calibrated for the effective value of the sine wave, and the measurement error of the square wave is extremely large. Therefore, the multimeter cannot accurately measure the output voltage of the active crystal oscillator, and can only indirectly determine whether it is oscillating through the DC range.
Rough measurement using the DC voltage range of the multimeter
Steps:
①. Adjust the multimeter to the DC voltage range (DC Voltage), connect the red probe to the crystal oscillator output pin, and the black probe to the ground (GND).
②. If the output is a square wave, the DC voltage value is approximately 50% of the supply voltage (Vcc) (for example: when the power supply is 3.3V, it displays approximately 1.65V).
③. The average voltage of the square wave is the middle value between the high level and the low level, but this method cannot reflect the true peak-to-peak value.
④. It can only preliminarily determine whether the crystal oscillator is oscillating (if the voltage is close to Vcc or 0V, the crystal oscillator may be damaged).
Correct measurement tool - oscilloscope:
You can directly observe the peak-to-peak value (Vpp), frequency and duty cycle of the waveform.
Oscilloscope setting suggestions:
1. The probe ground wire should be as short as possible to avoid introducing noise.
2. Set the trigger mode to "edge trigger" and the trigger level to the middle value of the signal amplitude.
Supplement:
The AC voltage range of ordinary multimeters usually only supports low frequencies (such as 50Hz~1kHz), while the frequency of active crystal oscillators is usually at the MHz level (such as 8MHz, 16MHz, 25MHz, etc.). High-frequency signals will cause the multimeter measurement value to be seriously low or even completely ineffective.
The output level is directly related to the input voltage. The YXC YSO110TR series is compatible with 1.8~3.3V.
